The present invention relates to a device for controlling a negative pressure in a suction pipe of an internal combustion engine.
Generally, the level of negative pressure in the suction pipe of an internal combustion engine is increased during deceleration of the engine to adversely affect an air-fuel ratio of the mixture, resulting in an increase of carbon monoxide component in the exhaust gas emitted from the engine.
As a countermeasure for overcoming this problem, Japanese Utility Model Publication No. 52-21411 entitled "A device for controlling exhaust gases during deceleration of engine" discloses a device for controlling the exhaust gas having a negative pressure control device adapted for introducing air into the air-fuel mixture at the downstream side of the throttle valve.
It is often experienced that the level of negative pressure in the suction pipe of an internal combustion engine is abruptly increased during deceleration of the engine to cause an excessive enrichment of the mixture. That is, a large amount of fuel is sucked into the engine in quite a short time of period. As a result, surplus fuel which can not be burnt in the combustion chamber of the engine is released into the exhaust pipe to be mixed with air in the outlet manifold, thereby causing an explosive combustion therein. This phenomenon is usually referred to as "after burning". At this time, carbon monoxide in the exhaust gas is suddenly increased.
In order to effectively prevent such after burning, it is necessary to mount an after burn valve in the suction pipe of the engine.
The "negative pressure device" disclosed in Japanese Patent Laid-Open Publication No. 52-115916 is a typical example of an after burn valve used for this purpose.
Thus, in order to maintain an adequate air-fuel ratio of the mixture during deceleration of the engine, it is necessary to use two separate devices comprising a negative pressure control device and an after burn valve.